Re: [BUG] `git gc` or `git pack-refs` wipes all notes for `git notes` command

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On Tue, Jan 3, 2023 at 11:04 AM Jeff King <peff@xxxxxxxx> wrote:

> That would be very surprising. The lookup of the ref in the notes code
> uses the same generic ref code that the rest of Git uses, which
> understands packed-refs and so on.

Thank you Jeff for looking at this also.

I tried to debug the issue by myself and found that the
`find_reference_location` function can't find the record for
`refs/notes/commits` in a repo.
I recall that a year ago I had trouble with a repo and it was damaged,
I restored it with the `git fsck` command and took some info from the
`git reflog`.
But somehow there was an issue in the `.git/packed-refs` file that was
there unexplored all past year.
The core of the issue I can demonstrate with two `.git/packed-refs` excerpts.

The issue excerpt:
```
dca1abdb5b870d46deae3717e87d0085b62d7242 refs/heads/tmp
d5ec01136b79a59a9e39d3ab02d92e1d91558579 refs/heads/tdf
c60f96a3f76e99e1b42f07204ad830c1483647b0 refs/heads/trunk
93119b80d4c7676a0ebe1bd6ae46574f96dfc7ed refs/notes/commits
452a23af3cfac6eef3bb1045894521fac8e51e2a refs/heads/cargo-config-toml
f5599d73873c451041fde857a09b5f12662357c1 refs/heads/custom
64076392359c4d4989320bde5712a8b389056f49 refs/heads/main
2119ff71ca66bec5117534907a127cee32680788 refs/heads/next
7e0016059ee7a87e3d04f7e59154529a9616a238 refs/recovery/1
de2876aa45022af815e717eb92becd61564efe32 refs/recovery/10
```

The correct excerpt:
```
dca1abdb5b870d46deae3717e87d0085b62d7242 refs/heads/tmp
d5ec01136b79a59a9e39d3ab02d92e1d91558579 refs/heads/tdf
c60f96a3f76e99e1b42f07204ad830c1483647b0 refs/heads/trunk
452a23af3cfac6eef3bb1045894521fac8e51e2a refs/heads/cargo-config-toml
f5599d73873c451041fde857a09b5f12662357c1 refs/heads/custom
64076392359c4d4989320bde5712a8b389056f49 refs/heads/main
2119ff71ca66bec5117534907a127cee32680788 refs/heads/next
93119b80d4c7676a0ebe1bd6ae46574f96dfc7ed refs/notes/commits
7e0016059ee7a87e3d04f7e59154529a9616a238 refs/recovery/1
de2876aa45022af815e717eb92becd61564efe32 refs/recovery/10
```

As you may notice that on the first except there is an issue with
sorting and after `ref/notes/*` there are several `ref/heads/*`.
So I suspect that the issue was introduced by myself a year ago when I
was recovering the repo.

> Can you share the .git directory of a repository that exhibits this
> behavior? It's possible there's a bug or something in the packed-refs
> code, though I find it pretty unlikely, as it's fairly well exercised in
> normal use.

The above excerpts completely describe the issue and there is no more
special in the repo.

I was surprised that such an issue can remain in the
`.git/packed-refs` for more than a year.
I thought that commands like `git fsck` would report such unordering
problems and `git gc` or `git pack-refs`
make ordering checks and make full resorting of the `.git/packed-refs`
file in case of issues with ordering.
I understand that the `.git/packed-refs` file is for machines and not
for humans but sometimes
it's the fastest way to make several simple corrections in it manually.

P.S: What was most surprising is that `git pack-refs` was able to
correctly update a hash even for an unordered record.

-Andrew



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